Facsimile transmitting and receiving system



Feb. 20, 1940. DURKEE 2,191,057

FACSIMILE TRANSMITTING AND RECEIVING SYSTEM Filed July 25, 1938 2Sheets-Sheet 1 INVENTOR.

Jame/0P3 BY Feb. 20, 1940. J. b. DURKEE 2,191,057

' FACSIMILE TRANSMITTING AND RECEIVING, SYSTEM Filed July 25, 1958 2Sheets-Sheet 2 m T INVENTOR. L

Patented Feb. 20, 1940 f I" i UNITED STATES PATENT OFFICE FACSIMILETRANSMITTING AND RECEIV- ING SYSTEM l James D. Durkee, Bartlesville,Okla, assignor to Phillips Petroleum Company, Bartlesville, kla., acorporation of Delawar e Application July 25, 1938, Serial No. 221,223

9 Claims. (Cl. 178-7.1)

My invention relates broadly to the transmisopen to frequencies at theone extremity of the sion and reproduction of facsimile pictures andband of frequencies, and substantially closed to more particularly to afrequency modulated audio frequencies at the other end of the band.

, frequency system. Other and further objects of my invention re- Thisapplication is a continuation-in-part of side in the circuits andarrangements hereinafter 5 my'application Serial Number 37,578, filedAugmore fully set forth with reference to the accomust 23, 1935, forFacsimile transmitting and repanying drawings, in which: Figure 1 is ascheceiving system. matic diagram of the circuit connections in the Inpicture transmitting systems wherein a ratransmitting system of myinvention; Fig. 2 is a 0 dio frequency carrier current is modulated insimilar schematic diagram of the circuit connecintensity directly by thevarying current from a tions in the receiving system of my invention;light sensitive cell, the varying tones in the picand Fig. 3 is aschematic circuit diagram of a ture being transmitted are registered toosharply modified form of the transmitter shown in Fig. 1. in thereproduced image, resulting in a facsimile The system of my inventioninvolves frequency of inferior quality. modulation within a relativelynarrow audio band 15 One of the objects of my invention is to proof abeat frequency resulting from the coaction vide a system of facsimilereproduction in which f a p a ty of high frequency OSCiIIotOI'S- e thelights and shadows in the original picture f q n y odu t d av s thenemployed, in are accurately reproduced, the preferred form of myinvention, to modulate Another object of my invention is to provide a aradiofrequency carrier current whereby the 2 modulating system whereinimpact excitations of modulations may be transmitted y Space radio thecarrier due to sharp changes in the intensity or line wire. At thereceiver, the radio frequency of the light focused on the photo-cell areelimicarrier current is rectified, and the detected varynated from themodulator output, and the signal ing audi f equ n y rr s are p y tcurrent caused to vary directly as the intensity of energize a li ht r ein intensity varying as 2 the light varies the modulations of the audiofrequency.

Still another object of my invention is to pro- The system of myinvention operates to transvide means for modulating a radio frequencycarmit the light variations in successive minute porrier current bymeans of an audio frequency wave, tions of the subj c picture A ScanningSystem the frequency of which is made to vary in aeat the transmitterand a synchronized system at 30 cordance with the light intensity ofsuccessive the receiver are accordingly required. These points in apicture to be transmitted. m y be f ny of the yp s wn n he A furtherobject of my invention is to provide the system f my inv n n e n onc n dprian intermediate audio frequency oscillator the marily With etransmission of the Varying Color frequency of which is modulated inaccordance tones in the subject p u with the variations in lightintensity in a picture Referring to the drawings in more detail, Fig. 1being scanned; the modulated audio frequency illustrates 1Jhetransmitting arrangement of my being employed to modulate the intensityof a invention. Reference character I indicates a radio frequencycarrier current for transmitting constant light source focused by lens 2on the by space radio or line wire the subject picture. l ght sensitivecell 3. A drum 4, carrying the film 40 A still further object of myinvention is to pro- 5 which bears the picture to be transmitted is videan audio beat frequency oscillator, the freoved by u a mechanical means,including quency of which is modulated by varying the a motor 5, so thatthe light beam from the source frequency of one of the componentfrequencies, 1 passesthreugh Successive minute p o s of to modulate aradio frequency carrier current. h fi being V d n t s y with the den- 45Still another object 'of my invention is to prosity of the film a denergizing the light Sensitive vide a translating system for detectingthe frecell 3 according yquency modulated audio wave and employing theThe Cell 3 s Connected in lJhe pu c rcuit modulations thereof to actuatea recording means f an e ron tu e a plifier stage 1, the output bychanging the intensity of a light source. of which is fed to anelectromagnetic device 50 A still further object of my invention is to psing a magnetic core structure 8 and an provide a filter device in thetranslating system armature 9, 1 W ch is Wound a coil l0 conresponsivein uniformly varying effect over the nected in the output circuit of theamplifier 1. band of frequencies over which the frequency The armature 9is mechanically connected by modulation extends, the filter beingeffectively means of shaft I 2 with the movable section Ma 55 of aVariable condenser It which is connected in the circuit of a highfrequency oscillator l5 and operable to vary the frequency of theoscillations generated therein.

A similar high frequency oscillator 16 has its output coupled with theoutput of the oscillator i5 in the combining circuit ll. Oscillators l5and it are preferably normally adjusted to operate at the same frequencyand to produce a zero beat in the combining circuit i'l. Oscillators l5and iii may, however, be adjusted so as normally to produce any desiredfundamental beat frequency. The combining circuit l1 includes thesecondaries of coupling transformers H and 22, the primaries of whichare connected in the output circuitsof the oscillators I5 and I6,respectively. As indicated in Figs. 1 and 3, these transformers,carrying high frequency currents from the oscillators, have asubstantial amount of iron in the cores flu, and 22a, saturable atthehigh frequencies of the oscillators so that the transformers havenon-linear frequency responsive characteristics. Connected in the seriescircuit l'l, the secondaries of these transformers H and 22 comprise acombination having a non-linear characteristic, wherein the outputcurrents of the oscillators l5 and it beat and result in a zero or lowfrequency beat wave to which the circuit H is linearly responsive. Asthe condenser M connected in circuit with oscillator I5 is varied by theelectromagnetic means controlled by the variations of light on the cell3, the frequency of the oscillations produced in oscillator I5 ismodulated according to the light variations on the cell 3. The beatfrequency, which is of audible magnitude, appearing in the combiningcircuit i'l likewise varies in accordance with the fluctuations inintensity of the light focused on the cell 3.

The combining circuit H is connected with a filter circuit 58 having thedual function of first excluding the higher fundamental harmonicfrequencies of the component oscillations issuing from the oscillatorsit, It, and second of passing currents of beat frequency, within theband covered by the modulations introduced by the condenser it, invarying intensities depending upon the instantaneous frequency of thewave. That is, the frequencies at one end of the band will be passedWithout diminution of the intensity of the current, while thefrequencies at the other end of the band will be substantiallysuppressed and currents at those frequencies correspondingly diminshed,the current passed by the filter l8 decreasing uniformly withproportionate changes in the frequency thereof. In other words, thefrequency modulations and the current passed by the filter vary in astraight line relation.

The filter i8 is coupled with an electron tubeamplifier it so that thevoltage on the grid thereof is directly proportional to the magnitude ofthe beat frequency and, accordingly, to the intensity of the light onthe cell 3. The output of amplifier i9 is employed to modulate a highfrequency carrier wave produced in an oscillator at 21], the modulationconsisting of. the beat frequency wave which varies not only infrequency but also in magnitude with the light intensity signal. Themodulated carrier is fed to a radiating system including antenna 2i andground 23.

At the receiver the modulated radio frequency carrier current isintercepted in the usual manner by tuningto the frequency of the carriercurrent, by means of the resonant circuit 24, Fig.

2, and rectified in the usual manner in a detector 25. The audiofrequency modulations thus detected are amplified in the electron tubestage 26 and fed into an audio frequency band pass filter 2? whichtransmits currents of all fre quencies within its range substantiallyuniformly. Further amplification may be obtained in the electron tubestage 3? from which the energy is fed to a source of light, such as aneon lamp, at 28, the intensity of the light produced thereby varyingwith the magnitude of the applied voltage. The light is focused by lensEli upon the light sensitive film (iii which is fixed on a drum l drivenby synchronized scanning means including motor 3.

Assuming that the beat note produced at the transmitter in the combiningcircuit ll, Fig. l, Varies between 500 and 1000 cycles, a plurality ofbeat frequency oscillators may be connected for multiplex operation,each employing a range of frequencies independent'from the others. Acorresponding plurality of filter systems Z'l may be provided at thereceiver, each operative over a predetermined band in cooperation withthe ranges of heat frequencies selected at the transmitters.

Fig. 3 shows a modified form of transmitter employing electrostaticmeans for varying the frequency of the component oscillator H5, in placeof the electromagnetic control means and a variable condenser shown inFig. l. The electro static device 3i may be the operative unit of acondenser microphone, in which case the electron tube in amplifier stagei should have a high impedance output circuit. The plate voltage of thetube acts as a biasing potential on the condenser plates, and variationsin the instantaneous voltage across a resistor 32 in the output circuitof the tube due to the variations in light intensity on thephotoelectric cell 3 will be effective directly as changes in capacity.The condenser device 3| is coupled to the circuit of the high frequencyoscillator it through condensers 3t and 35, and connected with the lowfrequency amplifier stage i by choke coil 35 in order to confine thehigh frequency currents from the oscillator l5 to the condenser plates.The condenser device 3| will thus be acted upon by the voltages acrossthe resistor 32, and function, in place of the variable condenser itshown in Fig. i, to modulate the frequency of the oscillator iii, Awider frequency band will be required using the circuit of Fig. 3 thanis possible with that of Fig. 1, as the diaphragm of a condensermicrophone will respond to frequencies as high as 10,300 cycles persecond, but greater sharpness of definition in the facsimile willbeassured,

A further modification of Fig. 1 shown in Fig; 3 is the provision of anelectron tube stage at 38 operative as a detector wherein theoscillations from oscillators i5 and i6 beat. The outputs of theoscillators I5 and itv are coupled by conventional transformer means tothe circuit at IT connected with the input of detector 38. The output ofthe detector is applied to the filter I8,

as is the beat frequency output of the combining circuit l! in Fig. l,and the filter it functions as hereinbefore described to pass current inproportion to the beat frequency. The remainder of the circuit issimilar to that of Fig. l. The electron tube detector stage 38 may beprovided in the arrangement of Fig. 1 in lieu of the nonlineartransformer devices comprising the combining circuit IT to effect thesame results, if desired. It will be noted,however, that the filter sand itstwo-fold function are featured in both circuitsand is anessential element of the system of my invention;

The transmission method of my invention prosults in no impactexcitations such as result from direct'modulation of the carrier. Freedfrom the impact excitations which extend over a relatively broad spacein the frequency spectrum, the-system of my invention is capable oftransmitting a number of pictures in the band width heretofore requiredfor the transmission of a single picture.

While I have described my invention in certain of its preferredembodiments, I desire that it be understood that modifications may bemade by those skilled in the art, and that no limitations upon myinvention are intended other than may be imposed by the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is as follows:

1. In an image transmitting system, the method of transmittingvariations of light intensity which comprises generating a beatfrequency wave by the coaction of two independent oscillations,modulating the frequency of one of the independent oscillations andthereby modulating the beat frequency, regulating the amplitude of thebeat frequency wave in accordance with the frequency of the same,generating a radio frequency carrier current, modulating the radiofrequency carrier current by the beat frequency wave, detecting themodulated radio frequency carrier to reestablish the modulated beatfrequency, employing the modulated beat frequency to vary the intensityof a light beam in accordance with the amplitude of the beat frequency 1wave, and recording the varying intensities of the light beam.

2.'In an image transmitting system of the type described, the method ofmodulating a radio frequency carrier current which comprises initiallymodulating the frequency of an audio wave resulting from the coaction ofa pair of high frequency oscillations, regulating the amplitude of theaudio wave in accordance with the frequency thereof, and subsequentlyemploying the audio wave to modulate a radio frequency carrier current.

3. In an image transmitting system of the type described, the method ofmodulating a radio frequen-cy carrier current which comprises,generating a beat frequency wave by the coaction of two independentoscillations, modulating the frequency of one of the independentoscillations in accordance with color tone variation of a picture orobject and therebymodulating the beat frequency, regulating theamplitude of the beat frequency wave in accordance with the frequencythereof, and employing the beat frequency wave to modulate a radiofrequency carrier current.

4. In an image transmitting system, means for transmitting variations oflight intensity which include a beat frequency oscillator comprising apair of individual oscillation generators, and means for combining theoutputs of said generators to produce an oscillation of beat frequency;means connected in one of said oscillation generators and controlled inaccordance with color tone of a picture or object for varying thefrequency of said one oscillation generator, the frequency of said! beatfrequency oscillation being modulated accordingly; and an audiofrequency filter system connected with said combining means and adaptedto pass current in proportion to its frequency within the range of saidfilter 1 system. I

5. In an image transmitting system, a source of energy comprisingseparate oscillator circuits, means for modulating the frequency of. oneof said oscillator circuits in accordance with the lights and shades inthe image transmitted, the frequency of the other of said oscillatorcircuits being constant, transformer means in the output of each of saidoscillator circuits and having nonlinear frequency responsivecharacteristicsin the range of frequencies of said oscillator circuits,

, said transformer means having secondary winda relatively low value andvariable in accordance with the initial modulation of the first saidosclllator circuit, a filter system connected with said combiningcircuit and operative to pass current of the beat frequency inproportion to its frequency, and means for modulating a carrier currentin accordance with the output, of said filter system.

6. In an image transmitting system, means for modulating a carriercurrent in accordance with the lights and shades in the imagetransmitted, which include a beat frequency circuit fed by separateoscillator circuits, the frequency of one of said circuits being variedby the light intensity signal while the frequency of the other of saidcircuits is constant, said beat frequency circuit comprising thesecondary windings of separate transformer means coupled with saidoscillator circuits and having non-linear frequency responsivecharacteristics in the range of frequencies of said oscillator circuits,and a filter system operative to pass currents of the modulation beatfrequency issuing from said beat frequency circuit in proportion to thefrequency thereof.

'7. In an image transmitting system, a beat frequency oscillatorconstituting means for relieving a carrier current of abrupt changes inmodulation due to impact excitation of a photo-cell by sharp changes inthelight intensity signal thereon, said beat frequency oscillatorcomprising separate oscillator circuits, the frequency of one of saidcircuits being varied by the light intensity signal While the frequencyof the other of said circuits is constant, and transformer meansconnected in the output of each of said oscillator circuits and havingnon-linear frequency responsive characteristics in the range offrequencies of said oscillator circuits, said transformer means havingsecondary windings connected in series combining circuit.

l 8. In an image transmitting system, a beat frequency oscillatorinterposed between photo-electric modulating means and a carriermodulating circuit, said beat frequency oscillator including a combiningcircuit inductively coupled with separate oscillator circuits and havinga non-linear frequency responsive characteristic in the range offrequencies of said oscillator circuits and a linear frequencyresponsive characteristic inthe range of the beat frequencies, thephoto-electric modulating means being arranged to modulate the frequencyof one of said oscillator circuits in accordance with color tonevariation of a picture or object, and means connected with saidcombining circuit for translating variations in the beat frequency intocurrent variations for said carrier modulating circuit.

9. In an image transmitting system, photoelectric scanning means, asource of alternating current controlled in frequency by said scanningmeans in accordance with light intensity in the object scanned, andmeans for regulating the amplitude of the alternating current from saidsource in accordance with the frequency thereof, said current ofvariable frequency being employed to modulate a carrier Wave and theamplitude variations of said current being adapted to control theintensity of a light beam for producing 10 an image of the objectscanned.

JAMES D. DURKEE.

. I CERTIFICATE OF CORRECTION. Patent No. 2,191,057. February 20, 1 1p.

JAMES D. DURKEE It 15 hereby certified that error appears .in theprinted apecificaticn of the above numbered patent requiring correctionas follows Page 5, first column; line 71+, claim L after the word"ton'e'! insert variation; and that the said Letters Patent should beread'with this correction therein that the same may conform to therecord of the case in the Patent Office.

Signed: and sealed this 2nd day of April, A. D. 191 0.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

